1. Field of the Invention
The present invention relates to an information processing system connected by radio communication between a host unit, such as a host computer, and a slave unit performing a discrete process, such as a printing process, so that data can be transmitted therebetween on carrier waves, such as radiowaves, supersonic waves or light beams. This invention also relates to a method of controlling such a system, and may be applied to various systems, particularly those composed of a plurality of host units and one or more slave units.
2. Description of the Related Art
Information processing systems have hitherto been connected by wire to peripheral units near these systems. Public or private lines are necessary to connect the information processing system to the peripheral units in remote areas. It has become possible in recent years to use radio communication to connect host units to slave units, both types of units constituting an information processing system, and consequently, to arrange various units remote from the host units. However, as connection by radio communication proliferates, various disadvantages occur.
Problems will be described below, especially those pertaining to an information processing system composed of a host computer and a printing system. Similar problems may also occur in other types of information processing systems.
When a printing system is constructed in which a printing system is connected by wire to a host computer, the printing system is disposed near the host computer. Because of such arrangement, the user does not have much trouble turning electric power (hereinafter written simply as power) to the printing system on and off.
However, in most cases, the printing system capable of radio communication is arranged in an area remote from the external unit serving as a host computer and within a distance where data can be transmitted to and from the external unit.
In such a case, the operator at the host computer must go to the printing system to turn the power to the printing system on and off before and after a printing process is performed. Such an operation is very complicated, and if the printing process is interrupted for a long period of time, electricity is wasted and therefore cannot be saved.
The printing system, one of the slave units constituting the above information processing system, prints all data transmitted from the host computer.
When a plurality of printing systems are arranged near the host computer, these systems simultaneously start to print data sent from the host computer. To avoid such a disadvantage, it is necessary to provide a means for specifying the printing systems. It is possible to employ a method in which reception frequencies are provided to printing systems which frequencies are specific to such systems. However, the reception frequencies cannot be provided to all printing systems because of the limited number of frequency bands.
When a general-purpose printing system, a type of slave unit in the above information processing system, receives data through radiowaves or another medium and performs a printing process, data interpreting portions are changed by switches on a panel in accordance with the frequency of a carrier wave (first method), or are changed by a command, for switching the data interpreting portions, contained in data (second method).
However, the first method is inconvenient because when the information processing system is controlled by radiowaves in a remote-control manner, the operator must go to the switches on the panel of the printing system remote from the host computer. Since the second method cannot switch the data interpreting portions until the above command is recognized, it is necessary to previously determine which data interpreting portion is operating.
Though the data interpreting portions are provided in accordance with language systems, it is difficult for printing systems with different language systems to have a common switching command.